Stabilization of wax acid greases by means of diphenol sulfides



STABILIZATION OF WAX ACID GREASES BY I MEANS OF DIPHENOL SULFIDES William H. Goff, Port Arthur, Tex., assignor to Texaco Inc., a corporation of Delaware No Drawing. Filed Apr. 10, 1957, Ser. No. 651,819

. Claims. Cl. 252-40) V This invention relates to lubricating greases containing soaps of oxidized petroleum fractions and to a method of stabilizing such greases. More particularly, it relates to the stabilization of greases thickened with petroleum oxidate soaps by means of compounds of the class of diphenol sulfides.

Lubricating greases prepared from oxidized petroleum fractions as the saponifiable materials have the disadvantage of undergoing discoloration and surface crusting in storage, which greatly impairs their utility andmarketability. Attempts which have been made heretofore to stabilize these greases against these changes by means of inhibitors of various types which are commonly employed in conventional lubricating greases have not been entirely successful, and the problem is complicated by the undesirable effects which many of the inhibitors have upon other properties of these greases, such as their texture or consistency.

It has now been found that greases prepared from oxidized petroleum fractions are very successfully inhibited against both surface crusting and discoloration during storage by means of small amounts of alkylated diphenol sulfides of the type represented by the formula HO OH wherein the groups represented by R are lower alkyl groups containing from 1 to about 6 carbon atoms and the groups represented by R are secondary or tertiary alkyl groups containing from 3 to about 8 carbon atoms. The groups represented by R are preferably tertiary alkyl groups containing from 4 to 5 carbon atoms. Compounds of this class include, for example, 4,4 thio bis (3-ethyl-6-sec. amyl phenol), 4,4 thio bis (3-hexyl-6-tert. butyl-phenol) and 4,4 thio bis (6-tert. butyl meta cresol). These compounds are obtained by well known reactions, such as, for example, by reacting suitable 3, 6-dialkyl phenols with sulfur dichloride.

The above compounds may be employed in petroleum oxidate greases in amounts from about 0.5 to about 5 percent by weight. They are preferably employed in amounts from about 1 to about 3 percent by weight, based on the weight of the grease.

The greases wherein these inhibitors are employed comprise essentially an oleaginous liquid thickened to a grease consistency by a metal soap of a saponifiable petroleum oxidate. The metal component of the oxidate soap may be any of the metals which are commonly employed in grease making, such as sodium, potassium, lithium, calcium, barium, magnesium, aluminum, lead and so forth. The preferred metals are those of the alkali metal and alkaline earth metal groups. The grease will ordinarily contain from about 5 to about 45 percent Pjatented Mar. 7, 1961 by weight of the petroleum oxidate soap, In addition, it may contain other thickening agents such as finely divided solids or other soaps, such as those prepared from the conventional fatty acids or hydroxy fatty 'acids.- a

The oxidates employed in preparing the greases of this invention are oxidized petroleum fractions containing considerable proportions of saponifiable materials, such as have been employed heretofore in grease making. They are obtained by oxidizing a petroleum fraction such as a lubricating oil fraction, crude or refined wax, slack wax or petrolatum at elevated temperatures by means of an oxidizing agent such as air or oxygen, in the pres- :nce or absence of a catalyst. The preferred oxidate is a material obtained by the oxidation of a petroleumwax having a saponification number in the range from about 100 to about 500. The oxidate fraction is employed in the grease making inany convenient manner by saponification with a suitable metal compound such as oxide, hydroxide or carbonate of an alkali metal or alkaline earth metal. The saponification is conveniently carried out in situ in a minor portion of the oleaginous liquid employed in the grease.

The oleaginous liquid employed in these greases may be any oils suitable for use in grease making generally, such as mineral oils obtained by any of the conventional refining processes in the lubricating oil viscosity range, preferably those having viscosities from about seconds Saybolt Universal at F. to about 225 seconds at 210 F. For certain purposes, such as for producing greases suitable for high temperature operations, various synthetic oils may be employed with advantage, such as high molecular weight ethers, esters and silicone polymer oils. Particularly suitable snythetic esters are the dicarboxylic acid esters, such as, for example, di-Z-ethyl- 'hexyl sebacate, disecondary amyl sebacate and xii-2- ethylhexyl azelate.

ther disclosing the invention.

EXAMPLE A grease was prepared in accordance with this invention comprising a mineral lubricating oil thickened with about 24.7 percent by weight of a sodium-calcium soap of a wax oxidate and containing 1.5 percent by weight of 4,4 thio bis (6-tertiary butyl meta cresol) as an inhibitor.

The wax oxidate employed as the saponifiable material in the grease preparation had a neutralization number of 190, a saponification number of 306 and contained about 20 percent of unsaponifiables. It was obtained by oxidizing a paraflin wax obtained from a pressed distillate of SAE 10 grade. The oxidation was carried out at a temperature of 270 F., a pressure of 65 p.s.i.g. and

The oil base was a blend consisting of 70 percent by a weight of a refined naphthene base residual oil having a Saybolt Universal viscosity at 210 F. of about 164 and 30 percent by Weight of a refined parafiin base distillate oil having a Saybolt Universal viscosity at 100 F. of about 99.

The grease preparation was carried out by saponifying the wax oxidate with a mixture of sodium hydroxide in aqueous solution and lime in suitable proportions to give a 6040 ratio of sodium and calcium soaps, in the presence of about 6 of the mineral oil employed in the grease. The charge was heated to 200 F. to complete the saponification and the temperature then increased to about 300 F. to dehydrate, after which the mass was allowed to cool while the remainder of the mineral oil was added gradually. The inhibitor was added to the grease at a temperature of about 150 F. A smooth slightly stringy grease was obtained having an ASTM penetration at 77 F. of 334 unworked and 344 worked 60 strokes) {The following table shows the storage'stability characteristics of this grease in comparison with thoseof-the .uninhibited grease, and also with those of the same grease containing other inhibitors of various types which are commonly employed in greases and other composioccurred. Table I ASTM Pena, worked 60 s. No. Inhibitor Appearance Original After 1 year 1.. none 344 360 Very hard thin brown crust.

2 1.5% of phosphorus-con- 407 375 Hard brown taining hydrocarbon; crust, oil commercial oxidation, pockets. polymerization and condensation inhibitor.

3 1.5% of -25 alkyl salicylic 374 373 Heavy brown acid. waxy crust.

4.. 1.5% of phenol mixture; 349 352 Black surface commercial anti-skinlayer. niug agent.

6... 1.5% oi N,N-disecondary 347 363 A inch very butyl-p-phenylenediblack surface amine. layer.

6-..... 1.5% ofdi-(Z-benzothiazyl- 406 398 Dark surface.

thiomethyl) urea.

7... 1.35% oimixturc of sodium too soft too soft No crust; or

salts of dithiocarbamic for pane. for pene. discoloraacid and Z-mercaptotion. benzothiazole; commercial oxidation inhibitor.

.8".-. 1.5% of 4,4. thio bis (otert. 341 342 Do.

butyl meta cresol).

As shown by the above data, the inhibitor ofthis invention prevented any crusting or discoloration of the waxate grease during storage for one year, and in addition no change in the worked penetration of this grease occurred. The other compounds, which are representative of a large number of inhibitors of difierent chemical types which were tested, either failed to prevent crusting or discoloration or they produced anundesirable softening of the grease on the basis of the worked penetration.

Obviously many modifications and variations of the invention as hereinbefore set forth maybe made without departing from the spirit and scope thereof and only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A lubricating grease which normally undergoes surface crusting and discoloration in storage consisting essentially of a mineral lubricating oil thickened to a grease consistency by about 5-45 percent by weight based on the composition of a metal soap of a saponifiable material obtained by the oxidation of a petroleum fraction wherein the said metal is chosen from the group consisting of alkali metals, alkaline earth metals and mixtures thereof, and wherein said surface crusting and discoloration are inhibited by about 0.5-5.0 percent by weight of a compound represented by the formula wherein R is an alkyl group containing 1-6 carbon atoms and R is selected from the group consisting of secondary and tertiary alkyl groups containing 3-8 carbon atoms.

2. 'The grease composition of claim 1 wherein R is a methyl group and R is a tertiary alkyl group containing 4-5 carbon atoms.

3. The grease composition of claim 1 wherein the said saponifiable material is a wax oxidate having a saponification number in about the range -500.

4. The grease composition of claim 1 wherein the metal component of the said soap is chosen from the group consisting of sodium, calcium, and mixtures thereof.

5. A lubricating grease which normally undergoes surface crusting and discoloration in storage consisting essentially of a mineral lubricating oil thickened to a grease consistency with about 5-45 percent by weight of a mixed base sodium-calcium waxate soap and wherein said surface crusting and discoloration are inhibited by about 0.5-5 percent by weight of 4,4 thio bis (6-tcrtiary butyl meta cresol).

References Cited in the file of this patent UNITED STATES PATENTS 

1. A LUBRICATING GREASE WHICH NORMALLY UNDERGOES SURFACE CRUSTING AND DISCOLORATION IN STORAGE CONSISTING ESSENTIALLY OF A MINERAL LUBRICATING OIL THICKENED TO A GREASE CONSISTENCY BY ABOUT 5-45 PERCENT BY WEIGHT BASED ON THE COMPOSITION OF A METAL SOAP OF A SAPONIFIABLE MATERIAL OBTAINED BY THE OXIDATION OF A PETROLEUM FRACTION WHEREIN THE SAID METAL IS CHOSEN FROM THE GROUP CONSISTING OF ALKALI METALS, ALKALINE EARTH METALS AND MIXTURES THEREOF, AND WHEREIN SAID SURFACE CRUSTING AND DISCOLORATION ARE INHIBITED BY ABOUT 0.5-5.0 PERCENT BY WEIGHT OF A COMPOUND REPRESENTED BY THE FORMULA 